[242] Mission control
begins when launch processing ends. At the point a missile is
committed to flight-as when the Shuttle solid rockets are fired or
a liquid-fueled booster rises an inch off the pad-responsibility
for monitoring and control of the spacecraft shifts from the
launch director and his crew to the flight director's team. Three
major tasks occupy the flight controllers: sampling the telemetry
stream to make certain everything is going well and to collect
science data, doing navigation calculations, and sending commands.
Manned and unmanned spacecraft require this support, with manned
spacecraft having the advantage of carrying observers and decision
makers to supplement what can be done from the ground. To
successfully support both types of missions, digital computers
must operate on massive amounts of data in real time. Mission
control tasks are beyond the abilities of humans alone.

Mission control centers and their
equipment are located far from the launch site. NASA's manned
mission control began in 1961 with Project Mercury at the Cape
Canaveral launch area, but its computers were at Goddard Space
Flight Center near Washington, D.C. Since 1964, early in the
Gemini program, both computers and controllers have been housed in
Building 30 at the Johnson Space Center in Houston. NASA's
unmanned near-earth missions are controlled mostly from Goddard,
with most deep space missions handled through the Jet Propulsion
Laboratory's (JPL) Spaceflight Operations Facility in Pasadena,
California.

In addition to control centers, mission
support requires numerous tracking stations to collect and format
telemetry and radar data to help in monitoring and navigation and
to transmit commands. These widely scattered stations and the
control centers are linked together by the NASA Communications
Network (NASCOM), headquartered at Goddard. The Space Tracking and
Data Acquisition Network (STADAN), used to specialize in unmanned
spacecraft but, having combined with the Manned Spaceflight
Network (MSFN) in 1972, has become the general network. When all
the specified Tracking and Data Relay Satellites are in place,
they will take over much of the manned flight communications, yet
tracking is still a STADAN responsibility. Lunar and planetary
probes are the venue of the Deep Space Network, which operates
three main stations at Goldstone, California, Madrid, Spain, and
Canberra, Australia, each with a variety of antennas ranging up to
64 meters in diameter. The Deep Space Network helped with manned
lunar missions when the Apollo spacecraft [243] passed a
distance of 10,000 miles from earth*.

In contrast with on-board computers,
computer systems used in control centers and tracking stations
have primarily consisted of off-the-shelf equipment. NASA could
take this approach to procurement because, so far, adequate
processing power to achieve mission objectives has been available
in commercial systems. When mission control began in the late
1950s and early 1960s, software technology had not reached the
necessary level of sophistication. The prime contractor had to
develop completely new operating system software for the Vanguard,
Mercury, and Gemini programs, but was able to incorporate large
chunks of existing operating systems into those used for Apollo
and Shuttle, as well as some later deep space missions. This was
possible in part because experience and techniques learned from
designing the original operating systems were used in new
commercial products.

* For the story
of the tracking and communication networks, see William R.
Corliss, Histories of the Space Tracking and Data Acquisition
Network (STADAN), the Manned Space Flight Network (MSFN). and the
NASA Communications Network (NASCOM), NASA CR-140390, June, 1974,
and N.A. Renzetti, ed., A History of the Deep Space Network From
Inception to January 1, 1969. Jet Propulsion Laboratory TR
32-1533, September 1, 1971. Each has considerable detail about the
technical developments involved, including the decision to use
computers at stations.